a. Field of the Invention
The instant disclosure relates generally to medical devices. In particular, the instant disclosure relates to elongate medical devices configured to buckle upon application of a critical force.
b. Background Art
Electrophysiology catheters are used in a variety of diagnostic, therapeutic, and/or mapping and ablative procedures to diagnose and/or correct conditions such as atrial arrhythmias, including for example, ectopic atrial tachycardia, atrial fibrillation, and atrial flutter. Arrhythmias can create a variety of conditions including irregular heart rates, loss of synchronous atrioventricular contractions and stasis of blood flow in a chamber of a heart which can lead to a variety of symptomatic and asymptomatic ailments and even death.
Typically, a catheter is deployed and manipulated through a patient's vasculature to the intended site, for example, a site within a patient's heart or a chamber or vein thereof. The catheter carries one or more electrodes that can be used for cardiac mapping or diagnosis, ablation and/or other therapy delivery modes, or both, for example. Once at the intended site, treatment can include, for example, radio frequency (RF) ablation, cryoablation, laser ablation, chemical ablation, high-intensity focused ultrasound-based ablation, microwave ablation, and/or other ablation treatments. The catheter imparts ablative energy to cardiac tissue to create one or more lesions in the cardiac tissue and oftentimes a contiguous or linear and transmural lesion. This lesion disrupts undesirable cardiac activation pathways and thereby limits, corrals, or prevents errant conduction signals that can form the basis for arrhythmias. According to at least one medical study (See, e.g., Ikeda et al., Radiofrequency Ablation Catheter with Contact Force Sensor Predicts Lesion Size and Incidence of Steam Pop in the Beating Canine Heart, Conference Proceedings of the Hearth Rhythm Society, May 2008 and Thiagalingam et al., Importance of Catheter Contact Force During Irrigated Radiofrequency Ablation: Evaluation in a Porcine Ex Vivo Model Using a Force-Sensing Catheter, Journal of Cardiovascular Electrophysiology, February 2010), the therapeutic force required to create a transmural lesion can be about 20 to about 50 grams-force.
To position a catheter within the body at a desired site, some type of navigation must be used, such as using mechanical steering features incorporated into the catheter (or an introducer sheath). In some examples, medical personnel may manually manipulate and/or operate the catheter using the mechanical steering features, and in other examples a robotic system may be used to manipulate and/or operate the catheter. Recent advances in the robotic control of catheters and the like allow advancement, retraction, and various deflections and/or steering to be controlled robotically.
In order to facilitate the advancement of catheters through a patient's vasculature, the simultaneous application of torque at the proximal end of the catheter and the ability to selectively deflect the distal tip of the catheter in a desired direction can permit medical personnel (either through manual operation or through robotic control) to adjust the direction of advancement of the distal end of the catheter and to position the distal portion of the catheter during an electrophysiological procedure. The proximal end of the catheter can be manipulated to guide the catheter through a patient's vasculature. The distal tip can be deflected by a pull wire attached at the distal end of the catheter that extends to a control handle or robotic system that controls the application of tension on the pull wire.
In catheter designs, it can be important to have sufficient flexibility in the catheter shaft to allow the catheter to follow the inherent curvature of the vasculature or endocardium without puncturing vascular tissue and/or cardiac tissue. The perforation of vascular tissue and/or cardiac tissue during cardiac mapping can be a problem in the practice of cardiac electrophysiology. A perforation in the cardiac tissue can result in pericardial effusion or the abnormal accumulation of fluid in the pericardial space and possible cardiac tamponade, which can be life threatening to the patient. The myocardium of the left atrium of the heart is particularly thin and is susceptible to perforation. According to at least one medical study (See, e.g., Shah et al., Catheter Tip Force Required to Mechanically Perforate the Cardiac Free Wall, Conference Proceedings of the Hearth Rhythm Society, May 2008), perforation of cardiac tissue can begin to occur with about 100 grams-force. However, other medical studies indicate that perforation of cardiac tissue may begin to occur with even less than about 100 grams-force.
Current catheter designs have concentrated on the use of force or contact sensing to carefully monitor and thereby limit the amount of force delivered during ablation in order to create safe and efficacious lesions. However, such force or contact sensing designs may not consistently provide completely accurate force measurements and can potentially register false positive detections of excessive force and false negatives in which excessive force is not preemptively avoided. Moreover, force or contact sensing systems may report a high force detection too late to prevent perforation. When a high force is generated, even if this force is reported instantaneously by the force or contact sensing systems, the damage may have been caused immediately giving the operator no opportunity to reduce the force.
There is therefore a need to minimize and/or eliminate one or more of the problems as set forth above. A preferable solution would be to avoid the problem of high catheter force altogether.